Flakey tachometer
Thread Starter
Cruising
Joined: Mar 2011
Posts: 12
Likes: 0
From: Otis or
Flakey tachometer
84 Corvette.
Digital dash works fine, except that the tach needs about twenty minutes to get warm enough to work. It reads "0" up till then. It's reading numbers, but nothing related to the engine turning.
Since it's started getting colder, the tach will finally come on and work and then every once in a while, it jumps up and down in the reading by 300-400 RPM.
I can just see something loose, I just don't know what it is. Any help?
Digital dash works fine, except that the tach needs about twenty minutes to get warm enough to work. It reads "0" up till then. It's reading numbers, but nothing related to the engine turning.
Since it's started getting colder, the tach will finally come on and work and then every once in a while, it jumps up and down in the reading by 300-400 RPM.
I can just see something loose, I just don't know what it is. Any help?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The early dashes are famous for having the solder joints go bad where the connectors attach to the PC boards. Start looking there. If you don't know what a cold solder joint looks like, call in an expert.
Another thing that happens is that the solder joints get hot because of the bad connection. You might see black areas in the PC board around the pins of the connectors.
Another thing that happens is that the solder joints get hot because of the bad connection. You might see black areas in the PC board around the pins of the connectors.
Drifting
Joined: Aug 2003
Posts: 1,565
Likes: 2
From: somewhere between heaven and hell WI
I would start under the hood. There is a port on the side of the tach that gets the reading for the dash. There is a red wire (that is power for the distributor) and the brown wire is for the tach. Remove that wire and check those terminals for corrosion. If they are dirty, cleans them with electrical contact cleaner or scrape them till shiny. That wire goes to a round thing that I think is the tach filter. Check that for bad/loose connections also.
Keep in mind, a wire can be broken internally and while the outer coating looks fine. I have had that problem several times on my 84. Feel the wire and bend it to feel if its broken or weak. Jiggle the wires around while someone watches the gauge for any difference.
Keep in mind, a wire can be broken internally and while the outer coating looks fine. I have had that problem several times on my 84. Feel the wire and bend it to feel if its broken or weak. Jiggle the wires around while someone watches the gauge for any difference.
Thread Starter
Cruising
Joined: Mar 2011
Posts: 12
Likes: 0
From: Otis or
Thanks gents. I've actually just put new bulbs in the dash, and had to replace the coil due to broken terminals. So both of those areas have been disturbed lately.
But the tach problem existed prior to that work, so doubt that I caused the problem.
Some solace anyway!
But the tach problem existed prior to that work, so doubt that I caused the problem.
Some solace anyway!
Instructor
Joined: Sep 2009
Posts: 182
Likes: 1
From: Greenville SC
You might want to look at your tach filter. I am not sure how to check it, but it's not expensive. My 84's tach didn't start working right until I put a new one on. Check Eckler's or Mid America, they are pretty common. Dave
